1. Field of the Invention
The present invention relates to an image display apparatus used in order to allow an observer to observe a two-dimensional image formed by an image forming device, and relates to a head mounted display (HMD) having the image display apparatus incorporated therein and including a frame shaped like glasses to be worn on the head of an observer.
2. Description of the Related Art
A virtual-image display apparatus (image display apparatus) in which a virtual-image optical system allows an observer to view, as an enlarged virtual image, a two-dimensional image formed by an image forming device is widely known from JP-A-2006-162767.
As shown in FIG. 1 that is a conceptual view, an image display apparatus 100 includes an image forming device 111 having a plurality of pixels arrayed in a two-dimensional matrix, a collimating optical system 112 for collimating light emitted from the pixels of the image forming device 111, and an optical device (a light guide means) 120 on which the light collimated by the collimating optical system 112 is incident. The incident light is guided and emitted from the optical device. The optical device 120 includes a light guide plate 121, a first deflecting member 130 (e.g., a single-layer light reflective film), and a second deflecting member 140 (e.g., a light reflective multilayer film having a multilayer laminated structure). Incident light propagates in the light guide plate 121 by total reflection and is then emitted from the light guide plate 121. The first deflecting member 130 reflects the light incident on the light guide plate 121 so that light incident on the light guide plate 121 is totally reflected in the light guide plate 121, and the second deflecting member 140 emits the light, which propagates in the light guide plate 121 by total reflection, from the light guide plate 121. For example, if HMD is formed by such an image display apparatus 100, the reduction in weight and size of an apparatus can be achieved.
Further, a virtual-image display apparatus (image display apparatus) using a hologram diffraction grating, in which a virtual-image optical system allows an observer to view, as an enlarged virtual image, a two-dimensional image formed by an image forming device is widely known from JP-A-2007-94175.
As shown in FIGS. 6A and 6B which are conceptual views, an image display apparatus 300 basically includes an image forming device 111 for displaying an image, a collimating optical system 112, and an optical device (a light guide means) 320 on which the light displayed by the image forming device 111 is incident. Incident light is guided to an eye 41 of an observer. Here, the optical device 320 includes a light guide plate 321, and first and second diffraction grating members 330 and 340 provided on the light guide plate 321. Each of the first and second diffraction grating members 330 and 340 is formed by a reflective volume hologram diffraction grating. Light emitted from pixels in the image forming device 111 enters the collimating optical system 112, where the light is converted into parallel light, and the parallel light enters the light guide plate 321. The parallel light is incident on and is emitted from a first surface 322 of the light guide plate 321. On the other hand, the first and second diffraction grating members 330 and 340 are attached to a second surface 323 of the light guide plate 321 parallel to the first surface 322 of the light guide plate 321.
A head mounted display that detects an angle at which the head mounted display is tilted from a horizontal level using an attitude sensor, and always holds a display image horizontally by image processing or a control driving device such as a motor is widely known from, for example, JP-A-2000-312319. By using the head mounted display having such a mechanism, even if the head of an observer is tilted, it is possible for the observer to observe a horizontal image.